Question

It has been hypothesized that people who are heterozygous for the allele that causes the deadly genetic condition cystic fibrosis (which, among other symptoms, reduces fertility) are more resistant to the deadly disease tuberculosis.

Suppose you travel to the future, to a time when neither cystic fibrosis nor tuberculosis have caused any deaths for many generations. In all of these future populations, the cystic fibrosis allele still exists at a low frequency.

Q10. You visit a huge city with millions of people. If you were to start sampling the cystic fibrosis allele from one generation to the next, what should happen to its frequency over the next few generations, and why?

The allele frequency should change a lot from one generation to the next due to random genetic drift.

The allele frequency should not change much from one generation to the next because the population is large.

The allele frequency should steadily increase due to natural selection.

The allele frequency should steadily decrease due to natural selection.

Answer 1

The allele is being transmitted from generation to the next generation in a heterozygous condition. The population is huge when we are sampling for the cystic fibrosis allele. There will be no natural selection acting on the population because no tuberculosis is present. If tuberculosis was present then the heterozygous individuals might have increased in number because they are resistant to tuberculosis, but in this study it is not the case as no tuberculosis is present. Hence no natural selection will be acting. The frequency of the allele will not change much because genetic drift occurs in a small population. But because the population is huge there is no genetic drift acting and hence the allele frequency wont be changing much.

Hence the correct answer is: The allele frequency should not change much from one generation to the next because the population is large.

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